Stress-Free Determination of Yield Locus and Flow Curve Parameters by Partial Full-Field Measurements

Full-field deformation measurement is used for many approaches in material characterization. To the best of our knowledge, optical measurement of the entire deformation field is not possible, regardless of the number of cameras used in the measurement system. There are always losses near the edges, so some assumptions are required to close these spots and restore the full-field measurement. The reason for these losses is the well-known problems of the subset-based DIC technique related to the sharp edges of samples cut from sheet materials. We believe that measuring the entire full-field is not even necessary for simultaneous calibration of the normalized yield locus curve and the normalized flow curve. The joint normalization of yield locus, flow curve and elastic modulus of a material with its initial yield stress results in the same deformation field as the original material model in a finite element simulation. The deformation field is thus purely related to the material parameters normalized in this way. This fact helps in simultaneous calibration of the normalized flow curve and the yield locus by using only a selected part of the deformation field without considering the stress distribution and force measurements. The obvious proof is given that the problem breaks down to pure geometry. This is followed by the details of the approach. Finally, a validation study with virtual experiments is presented.